linux-kernel - [PATCH v2 5/8] rcu/nocb: Wake up gp thread when flushing

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Date:   Wed, 22 Jun 2022 22:50:59 +0000
From:   "Joel Fernandes (Google)" <joel@...lfernandes.org>
To:     rcu@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, rushikesh.s.kadam@...el.com,
        urezki@...il.com, neeraj.iitr10@...il.com, frederic@...nel.org,
        paulmck@...nel.org, rostedt@...dmis.org, vineeth@...byteword.org,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Subject: [PATCH v2 5/8] rcu/nocb: Wake up gp thread when flushing

We notice that rcu_barrier() can take a really long time. It appears
that this can happen when all CBs are lazy and the timer does not fire
yet. So after flushing, nothing wakes up GP thread. This patch forces
GP thread to wake when bypass flushing happens, this fixes the
rcu_barrier() delays with lazy CBs.

Signed-off-by: Joel Fernandes (Google) <joel@...lfernandes.org>
---
 kernel/rcu/tree_nocb.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 2f5da12811a5..b481f1ea57c0 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -325,6 +325,8 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp,
 	rcu_segcblist_insert_pend_cbs(&rdp->cblist, &rcl);
 	WRITE_ONCE(rdp->nocb_bypass_first, j);
 	rcu_nocb_bypass_unlock(rdp);
+
+	wake_nocb_gp(rdp, true);
 	return true;
 }
 
-- 
2.37.0.rc0.104.g0611611a94-goog